// when you want to use "Color.Lerp" just once!
private float lerpControlVal = 0.0f;
void Update() {
        if (isLearping)
        {
            Color temp = Color.Lerp(blue, Color.black, lerpControlVal);
            initialMat.SetColor("_node_6523", temp);
            whaleRef.GetComponentInChildren<SkinnedMeshRenderer>().materials = mats_default;
            if (lerpControlVal < 1)
            {
                lerpControlVal += Time.deltaTime / 1.0f;
            } else
            {
                whaleRef.GetComponentInChildren<SkinnedMeshRenderer>().materials = mats_hide;
                isLearping = false;
                lerpControlVal = 0.0f;
            }
        }
    }